I was involved in a pond remediation of a gypsum stack collection pond. there was a lot of single cell algae growing in the pond at a pH of 1.4. the pond water was high in PO4 due to the nature of the run off from he phosphogypsum stack, but it grew algae big time. I think it depends on all water chemistry and not just pH. There is a small lake near Huntsville Texas that is extremely alkaline. It sits amid acres of pines. It is extremely clear and so is used for open water scuba tests. No fish or plants grow in the lake due to the high pH. It appears to be a natural soda ash deposit that causes the high pH and sterile condition. although it is clear, he water will cause your skin to dry and will irritate the eyes.
Depending on your finances, the best way to create a clear water pond might be to consider filtration. Coagulation and flocculation to enhance settling will work, but if you use for swimming, it will stir each time and need to be allowed to re-settle.

Mike